Hold the pulling tag of the slider and use the pliers to cut off the little bar at its top center part. This little bar is what holds the zipper slider together. Remove the old slider.
Attach the new slider to one side of the zipper by inserting the zipper through the hole. Move the slider up and down. Choose a spot near the starting position of the zipper to ensure the slider is going toward the right direction on the luggage.
Hold the other side of the zipper and fit through the second slider hole. Move up and down.